Add probe-disk and mount-fat interfaces.
Add probe-disk and mount-fat interfaces.

probe-disk - If the partition contains a FAT file system, return the
    Volume ID, otherwise NIL.

mount-fat - If the partition contains a FAT file system, determine the
    FAT type and register an appropriate host using the
    host-name. Returns the host-name.

froggey/Mezzano,froggey/Mezzano